HOME FIRE PROTECTION
Fireproofing the house including smoke detectors, fire escapes, evacuation plans, fire extinguishers.
A SMOKE DETECTOR CAN PROVIDE VITAL EARLY WARNING TO
PROTECT YOU AND YOUR FAMILY ...the perils of a
home conflagration
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by David Schoonmaker
EACH YEAR, BETWEEN 5,000 and 6,000 people in the U S. die
as a result of structural fires, ranking it fourth as a
cause of accidental death. Only car accidents, falls, and
drowning claim more lives. Of these fatalities, more than
80% occur in one- and two-family homes.
Happy, there are significant fewer fire deaths today than
there were 10 years ago—this despite more than a
doubling in property losses owing to fire during the same
period. There's a simple explanation for the declining
number of deaths in the face of increasing dollar losses.
It's called the smoke detector.
The Hardware
There are two basic types of smoke detectors. An ionization
unit contains a small amount (less than one microcurie) of
a radio-active substance, such as americium-241. The
decaying material fills one or two sampling chambers with
ions of nitrogen and oxygen, which support a very small
electrical current that keeps the alarm silent. Should
smoke enter the chamber(s), however, the ions attach to the
particles, and the current path breaks down, sounding the
alarm.
Photoelectric smoke alarms rely on light scattering to
detect smoke. As long as light emitted periodically by a
diode (LED) fails to strike a photocell set out of line of
the light path, the alarm stays off. But if smoke enters
the light-tight chamber, the particles will reflect and
refract the light onto the photocell, sounding the alarm.
Each type has its advantages. Because it depends on an
ion-strewn current path, the ionization detector responds
better to smoke consisting of numerous small (less than one
micron) particles—typical of the emissions from a
blazing fire. It will, for example, respond quickly to
toxic gases given off by certain burning plastics.
Unfortunately, it's also quite sensitive to the fumes
produced in a busy kitchen. A photoelectric detector
responds more quickly to the large (greater than one
micron) particles produced by smoldering fires. It will
warn earlier of the sort of fire caused by a careless
smoker or by spontaneous combustion, And it's much less
prone to sound nuisance alarms. Its main failing is a
comparative insensitivity to fumes and to black particles,
which absorb rather than reflect light.
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